1. Field of the Invention
The present invention relates to an optical transmission element, an image guide or a light guide which includes a plurality of the optical transmission elements, an endoscope including at least one of the image guide and the light guide, and a method for manufacturing the optical transmission element.
2. Description of the Related Art
In a conventional endoscope, a glass optical fiber is passed through an insertion portion of the endoscope in order to secure brightness during observation. Such an optical fiber is used to transmit illumination light toward a tip part from a light source.
The optical fiber has excellent transmissivity and light distribution properties. However, the optical fiber has high hardness and low flexibility in terms of physical properties. Since the tip part of the endoscope is repeatedly severely bent, the optical fiber is disadvantageously apt to break at the tip part. Since the endoscope is densely filled with the optical fibers, the optical fibers suffer from frictional contact also in portions other than the tip part, which disadvantageously causes the optical fibers to break. If the optical fiber in the endoscope breaks, a transmitted light amount is decreased, which causes deterioration in the observation performance of the endoscope.
An optical transmission element as an optical fiber for solving such a problem is disclosed in Japanese Patent No. 4229890. In the optical transmission element, a covering layer including a fluorine-substituted alkyl group-containing organic silicon compound (hereinafter, a fluorinated alkylsilane layer) is formed on the outer periphery of a fiber.